Biometric system with photoacoustic imaging

ABSTRACT

An apparatus may include an ultrasonic sensor array, a light source system and a control system. Some implementations may include an ultrasonic transmitter. The control system may be operatively configured to control the light source system to emit light that induces acoustic wave emissions inside a target object. The control system may be operatively configured to select a first acquisition time delay for the reception of acoustic wave emissions primarily from a first depth inside the target object. The control system may be operatively configured to acquire first ultrasonic image data from the acoustic wave emissions received by the ultrasonic sensor array during a first acquisition time window. The first acquisition time window may be initiated at an end time of the first acquisition time delay.

TECHNICAL FIELD

This disclosure relates generally to biometric devices and methods,including but not limited to biometric devices and methods applicable tomobile devices.

DESCRIPTION OF THE RELATED TECHNOLOGY

As mobile devices become more versatile, user authentication becomesincreasingly important. Increasing amounts of personal information maybe stored on and/or accessible by a mobile device. Moreover, mobiledevices are increasingly being used to make purchases and perform othercommercial transactions. Some mobile devices, including but not limitedto smartphones, currently include fingerprint sensors for userauthentication. However, some fingerprint sensors are easily spoofed.Improved authentication methods would be desirable.

SUMMARY

The systems, methods and devices of the disclosure each have severalinnovative aspects, no single one of which is solely responsible for thedesirable attributes disclosed herein.

One innovative aspect of the subject matter described in this disclosurecan be implemented in an apparatus. The apparatus may include asubstrate, an ultrasonic sensor array on or proximate the substrate, alight source system and a control system. In some examples, theapparatus may be, or may include, a biometric system. In someimplementations, a mobile device may be, or may include, the apparatus.For example, a mobile device may include a biometric system as disclosedherein.

The control system may include one or more general purpose single- ormulti-chip processors, digital signal processors (DSPs), applicationspecific integrated circuits (ASICs), field programmable gate arrays(FPGAs) or other programmable logic devices, discrete gates ortransistor logic, discrete hardware components, or combinations thereof.The control system may be capable of controlling the light source systemto emit light and of receiving signals from the ultrasonic sensor arraycorresponding to acoustic waves emitted from portions of a targetobject. The emissions may be due to the target object being illuminatedwith light emitted by the light source system. The control system may becapable of performing a user authentication process that is based, atleast in part, on the signals from the ultrasonic sensor array.

The apparatus may or may not include an ultrasonic transmitter,depending on the particular implementation. If the apparatus includes anultrasonic transmitter, the control system may be capable of controllingthe ultrasonic transmitter to obtain fingerprint image data via theultrasonic sensor array. The authentication process may involveevaluating the fingerprint image data.

In some examples, the light source system may include one or more laserdiodes or light-emitting diodes. For example, the light source systemmay include at least one infrared, optical, red, green, blue, white orultraviolet light-emitting diode and/or at least one infrared, optical,red, green, blue or ultraviolet laser diode. In some implementations,the light source system may be capable of emitting a light pulse with apulse width less than about 100 nanoseconds. In some examples, the lightsource system may be capable of emitting a plurality of light pulses ata pulse frequency between about 1 MHz and about 100 MHz. The pulsefrequency of the plurality of light pulses may, in some instances,correspond to an acoustic resonant frequency of the ultrasonic sensorarray and/or the substrate. According to some implementations, the lightemitted by the light source system may be transmitted through thesubstrate. According to some examples, the control system may be capableof selecting one or more acquisition time delays to receive acousticwave emissions from one or more corresponding distances from theultrasonic sensor array.

In some implementations, the control system may be capable of selectinga wavelength of the light emitted by the light source system. Accordingto some such implementations, the control system may be capable ofselecting the wavelength and a light intensity associated with theselected wavelength to illuminate portions of the target object.

According to some examples, the control system may be capable ofcomparing, for the purpose of user authentication, attribute informationwith stored attribute information obtained from image data that haspreviously been received from an authorized user. The attributeinformation may be obtained from received image data, based on thesignals from the ultrasonic sensor array. In some examples, theattribute information obtained from the received image data and thestored attribute information may include attribute informationcorresponding to at least one of sub-epidermal features, muscle tissuefeatures or bone tissue features. In some implementations, the attributeinformation obtained from the received image data and the storedattribute information may include attribute information corresponding tosub-epidermal features. In some such implementations, the sub-epidermalfeatures may include features of the dermis, features of the subcutis,blood vessel features, lymph vessel features, sweat gland features, hairfollicle features, hair papilla features and/or fat lobule features.Alternatively, or additionally, the attribute information obtained fromthe received image data and the stored attribute information may includeinformation regarding fingerprint minutia.

In some examples, the control system may be capable of, for the purposeof user authentication, obtaining ultrasonic image data viainsonification of the target object with ultrasonic waves from anultrasonic transmitter. The control system may be capable of obtainingultrasonic image data via illumination of the target object with lightemitted from the light source system. In some such examples, theultrasonic image data obtained via insonification of the target objectmay include fingerprint image data. Alternatively, or additionally, theultrasonic image data obtained via illumination of the target object mayinclude vascular image data.

According to some implementations, the target object may be positionedon a surface of the ultrasonic sensor array or positioned on a surfaceof a platen that is acoustically coupled to the ultrasonic sensor array.In some examples, the target object may be a finger or a finger-likeobject. According to some implementations, the control system may beconfigured to make a liveness determination of the target object basedon the received signals.

Other innovative aspects of the subject matter described in thisdisclosure can be implemented in a biometric authentication method thatmay involve controlling a light source system to emit light. The methodmay involve receiving signals from an ultrasonic sensor arraycorresponding to acoustic waves emitted from portions of a target objectin response to being illuminated with light emitted by the light sourcesystem. The method may involve performing a user authentication processthat is based, at least in part, on the signals from the ultrasonicsensor array.

In some examples, the method may involve obtaining ultrasonic image datavia insonification of the target object with ultrasonic waves from anultrasonic transmitter. The user authentication process may be based, atleast in part, on the ultrasonic image data.

In some instances, the method may involve selecting a wavelength and alight intensity of the light emitted by the light source system toselectively generate acoustic wave emissions from portions of the targetobject. In some examples, the method may involve selecting anacquisition time delay to receive acoustic wave emissions at acorresponding distance from the ultrasonic sensor array.

In some examples, controlling the light source system may involvecontrolling a light source system of a mobile device. In some suchexamples, controlling the light source system involves controlling atleast one backlight or front light capable of illuminating a display ofthe mobile device.

Some or all of the methods described herein may be performed by one ormore devices according to instructions (e.g., software) stored onnon-transitory media. Such non-transitory media may include memorydevices such as those described herein, including but not limited torandom access memory (RAM) devices, read-only memory (ROM) devices, etc.Accordingly, some innovative aspects of the subject matter described inthis disclosure can be implemented in a non-transitory medium havingsoftware stored thereon.

For example, the software may include instructions for controlling alight source system to emit light. The software may include instructionsfor receiving signals from an ultrasonic sensor array corresponding toacoustic waves emitted from portions of a target object in response tobeing illuminated with light emitted by the light source system. Thesoftware may include instructions for performing a user authenticationprocess that is based, at least in part, on the signals from theultrasonic sensor array.

According to some examples, the software may include instructions forobtaining ultrasonic image data via insonification of the target objectwith ultrasonic waves from an ultrasonic transmitter. The userauthentication process may be based, at least in part, on the ultrasonicimage data. In some instances, the software may include instructions forselecting a wavelength and a light intensity of the light emitted by thelight source system to selectively generate acoustic wave emissions fromportions of the target object. In some examples, the software mayinclude instructions for selecting an acquisition time delay to receiveacoustic wave emissions at a corresponding distance from the ultrasonicsensor array. According to some implementations, controlling the lightsource system may involve controlling at least one backlight or frontlight capable of illuminating a display of a mobile device.

Other innovative aspects of the subject matter described in thisdisclosure also can be implemented in an apparatus. The apparatus mayinclude an ultrasonic sensor array, a light source system and a controlsystem. In some examples, the apparatus may be, or may include, abiometric system. In some implementations, a mobile device may be, ormay include, the apparatus. For example, a mobile device may include abiometric system as disclosed herein. In some implementations, theultrasonic sensor array and a portion of the light source system may beconfigured in an ultrasonic button, a display module and/or a mobiledevice enclosure.

The control system may include one or more general purpose single- ormulti-chip processors, digital signal processors (DSPs), applicationspecific integrated circuits (ASICs), field programmable gate arrays(FPGAs) or other programmable logic devices, discrete gates ortransistor logic, discrete hardware components, or combinations thereof.The control system may be operatively configured to control the lightsource system to emit light that induces acoustic wave emissions insidea target object. The control system may be operatively configured toselect a first acquisition time delay for the reception of acoustic waveemissions primarily from a first depth inside the target object. Thecontrol system may be operatively configured to acquire first ultrasonicimage data from the acoustic wave emissions received by the ultrasonicsensor array during a first acquisition time window. The firstacquisition time window may be initiated at an end time of the firstacquisition time delay. In some implementations, the first ultrasonicimage data may be acquired during the first acquisition time window froma peak detector circuit disposed in each of a plurality of sensor pixelswithin the ultrasonic sensor array.

In some examples, the apparatus may include a display. The controlsystem may be configured to control the display to depict atwo-dimensional image that corresponds with the first ultrasonic imagedata.

According to some examples, the acquisition time delay may be measuredfrom a time that the light source system emits light. In someimplementations, the first acquisition time window may be in the rangeof about 10 nanoseconds to about 200 nanoseconds. In some instances, thecontrol system may be operatively configured to select second throughN^(th) acquisition time delays and to acquire second through N^(th)ultrasonic image data during second through N^(th) acquisition timewindows after the second through N^(th) acquisition time delays. Each ofthe second through N^(th) acquisition time delays may correspond to asecond through an N^(th) depth inside the target object. In some suchexamples, the apparatus may include a display and the control system maybe configured to control the display to depict a three-dimensional imagethat corresponds with at least a subset of the first through N^(th)ultrasonic image data.

In some examples, the light source system may include one or more laserdiodes, semiconductor lasers and/or light-emitting diodes. For example,the light source system may include at least one infrared, optical, red,green, blue, white or ultraviolet light-emitting diode and/or at leastone infrared, optical, red, green, blue or ultraviolet laser diode. Insome implementations, the light source system may be capable of emittinga light pulse with a pulse width less than about 100 nanoseconds.According to some implementations, the control system may be configuredto control the light source system to emit at least one light pulsehaving a duration that is in the range of about 10 nanoseconds to about500 nanoseconds. In some examples, the light source system may becapable of emitting a plurality of light pulses at a pulse frequencybetween about 1 MHz and about 100 MHz.

In some implementations, the apparatus may include a substrate. In somesuch implementations, the ultrasonic sensor array may be formed in or onthe substrate. In some examples, the light source system may be coupledto the substrate. According to some implementations, the light emittedby the light source system may be transmitted through the substrate. Insome examples, light emitted by the light source system may betransmitted through the ultrasonic sensor array. In someimplementations, the light emitted by the light source system mayinclude a plurality of light pulses and the pulse frequency of theplurality of light pulses may correspond to an acoustic resonantfrequency of the ultrasonic sensor array and/or the substrate. Accordingto some examples, the control system may be capable of selecting one ormore acquisition time delays to receive acoustic wave emissions from oneor more corresponding distances from the ultrasonic sensor array.

In some implementations, the control system may be capable of selectinga wavelength of the light emitted by the light source system. Accordingto some such implementations, the control system may be capable ofselecting the wavelength and a light intensity associated with theselected wavelength to illuminate portions of the target object. In someexamples, the control system may be configured to select one or morewavelengths of the light to trigger acoustic wave emissions primarilyfrom a particular type of material in the target object.

According to some examples, the control system may be capable ofcomparing, for the purpose of user authentication, attribute informationobtained from received image data, based on the signals from theultrasonic sensor array, with stored attribute information obtained fromimage data that has previously been received from an authorized user. Insome examples, the attribute information obtained from the receivedimage data and the stored attribute information may include attributeinformation corresponding to at least one of sub-epidermal features,muscle tissue features or bone tissue features. In some implementations,the attribute information obtained from the received image data and thestored attribute information may include attribute informationcorresponding to sub-epidermal features. In some such implementations,the sub-epidermal features may include features of the dermis, featuresof the subcutis, blood vessel features, lymph vessel features, sweatgland features, hair follicle features, hair papilla features and/or fatlobule features. Alternatively, or additionally, the attributeinformation obtained from the received image data and the storedattribute information may include information regarding fingerprintminutia.

In some examples, the control system may be capable of, for the purposeof user authentication, obtaining ultrasonic image data viainsonification of the target object with ultrasonic waves from anultrasonic transmitter. The control system may be capable of obtainingultrasonic image data via illumination of the target object with lightemitted from the light source system. In some such examples, theultrasonic image data obtained via insonification of the target objectmay include fingerprint image data. Alternatively, or additionally, theultrasonic image data obtained via illumination of the target object mayinclude vascular image data.

According to some implementations, the target object may be positionedon a surface of the ultrasonic sensor array or positioned on a surfaceof a platen that is acoustically coupled to the ultrasonic sensor array.In some examples, the target object may be a finger or a finger-likeobject. According to some implementations, the control system may beconfigured to make a liveness determination of the target object basedon the received signals.

According to some implementations, controlling the light source systemmay involve controlling at least one backlight or front light capable ofilluminating a display. The light source system may include at least onebacklight or front light configured for illuminating the display and atarget object. In some examples, controlling the light source system mayinvolve controlling a light source system of a mobile device. In somesuch examples, controlling the light source system involves controllingat least one backlight or front light capable of illuminating a displayof the mobile device.

In some examples, the control system may be configured to estimate ablood oxygen level. According to some implementations, the controlsystem may be configured to estimate a blood glucose level.

In some examples, the control system may be configured to acquire secondultrasonic image data primarily from the first depth inside the targetobject. In some instances, the second ultrasonic image data may beacquired after a period of time corresponding to a frame rate.

In some implementations, the control system may be configured for imagestitching. For example, in some such implementations, the control systemmay be configured to acquire second ultrasonic image data at primarilythe first depth inside the target object. The second ultrasonic imagedata may be acquired after the target object is repositioned on theapparatus or after the apparatus has been repositioned with respect tothe target object. In some implementations, the control system may beconfigured to stitch together the first and second ultrasonic image datato form a composite ultrasonic image.

The apparatus may or may not include an ultrasonic transmitter,depending on the particular implementation. If the apparatus includes anultrasonic transmitter, the control system may be configured to acquiresecond ultrasonic image data from insonification of the target objectwith ultrasonic waves from the ultrasonic transmitter. In some suchexamples, the second ultrasonic image data may be acquired primarilyfrom the first depth inside the target object and the first ultrasonicimage data and the second ultrasonic image data may be acquired from aplurality of sensor pixels within the ultrasonic sensor array. In someexamples, the control system may be capable of controlling theultrasonic transmitter to obtain fingerprint image data via theultrasonic sensor array. The authentication process may involveevaluating the fingerprint image data and/or evaluating date that isbased on the fingerprint image data, such as fingerprint minutiae.

Still other innovative aspects of the subject matter described in thisdisclosure can be implemented in a method of acquiring ultrasonic imagedata that involves controlling a light source system to emit light. Thelight may induce acoustic wave emissions inside a target object. Themethod may involve selecting a first acquisition time delay to receivethe acoustic wave emissions primarily from a first depth inside thetarget object. The method may involve acquiring first ultrasonic imagedata from the acoustic wave emissions received by a ultrasonic sensorarray during a first acquisition time window. The first acquisition timewindow may be initiated at an end time of the first acquisition timedelay. In some examples, the method may involve controlling a display todepict a two-dimensional image that corresponds with the firstultrasonic image data.

In some examples, the acquisition time delay may be measured from a timethat the light source system emits light. In some instances, the firstacquisition time window may be in the range of about 10 nanoseconds toabout 200 nanoseconds.

In some examples, the method may involve selecting second through N^(th)acquisition time delays and acquiring second through N^(th) ultrasonicimage data during second through N^(th) acquisition time windows afterthe second through N^(th) acquisition time delays. In some suchexamples, each of the second through N^(th) acquisition time delays maycorrespond to a second through an N^(th) depth inside the target object.

Yet other innovative aspects of the subject matter described in thisdisclosure can be implemented in a non-transitory medium having softwarestored thereon. In some examples, the software may include instructionsfor controlling one or more devices to control a light source system toemit light. The light may induce acoustic wave emissions inside a targetobject. The software may include instructions for selecting a firstacquisition time delay to receive the acoustic wave emissions primarilyfrom a first depth inside the target object. The software may includeinstructions for acquiring first ultrasonic image data from the acousticwave emissions received by a ultrasonic sensor array during a firstacquisition time window. In some examples, the software may includeinstructions for controlling a display to depict a two-dimensional imagethat corresponds with the first ultrasonic image data.

The first acquisition time window may, for example, be initiated at anend time of the first acquisition time delay. In some examples, theacquisition time delay is measured from a time that the light sourcesystem emits light. According to some implementations, the firstacquisition time window may be in the range of about 10 nanoseconds toabout 200 nanoseconds. In some examples, the software may includeinstructions for selecting second through N^(th) acquisition time delaysand for acquiring second through N^(th) ultrasonic image data duringsecond through N^(th) acquisition time windows after the second throughN^(th) acquisition time delays. Each of the second through N^(th)acquisition time delays may correspond to a second through an N^(th)depth inside the target object.

BRIEF DESCRIPTION OF THE DRAWINGS

Details of one or more implementations of the subject matter describedin this specification are set forth in the accompanying drawings and thedescription below. Other features, aspects, and advantages will becomeapparent from the description, the drawings, and the claims. Note thatthe relative dimensions of the following figures may not be drawn toscale. Like reference numbers and designations in the various drawingsindicate like elements.

FIG. 1 shows an example of components of blood being differentiallyheated by incident light and subsequently emitting acoustic waves.

FIG. 2 is a block diagram that shows example components of an apparatusaccording to some disclosed implementations.

FIG. 3 is a flow diagram that provides examples of biometric systemoperations.

FIG. 4 shows an example of a cross-sectional view of an apparatuscapable of performing the method of FIG. 3.

FIG. 5 shows an example of a mobile device that includes a biometricsystem as disclosed herein.

FIG. 6 is a flow diagram that provides further examples of biometricsystem operations.

FIG. 7 shows examples of multiple acquisition time delays being selectedto receive acoustic waves emitted from different depths.

FIG. 8 is a flow diagram that provides additional examples of biometricsystem operations.

FIG. 9 shows examples of multiple acquisition time delays being selectedto receive ultrasonic waves emitted from different depths, in responseto a plurality of light pulses.

FIGS. 10A-10C are examples of cross-sectional views of a target objectpositioned on a platen of a biometric system such as those disclosedherein.

FIGS. 10D-10F show a series of simplified two-dimensional images and athree-dimensional reconstruction that correspond with ultrasonic imagedata acquired by the processes shown in FIGS. 10A-10C.

FIG. 11 shows an example of a mobile device that includes a biometricsystem capable of performing methods disclosed herein.

FIG. 12 is a flow diagram that provides an example of a method ofstitching ultrasonic image data obtained via a mobile device such asthat shown in FIG. 11.

FIG. 13 is a flow diagram that shows blocks of a method of oxidizedhemoglobin detection that may be performed with some disclosed biometricsystems.

FIG. 14 representationally depicts aspects of a 4×4 pixel array ofsensor pixels for an ultrasonic sensor system.

FIG. 15A shows an example of an exploded view of an ultrasonic sensorsystem.

FIG. 15B shows an exploded view of an alternative example of anultrasonic sensor system.

DETAILED DESCRIPTION

The following description is directed to certain implementations for thepurposes of describing the innovative aspects of this disclosure.However, a person having ordinary skill in the art will readilyrecognize that the teachings herein may be applied in a multitude ofdifferent ways. The described implementations may be implemented in anydevice, apparatus, or system that includes a biometric system asdisclosed herein. In addition, it is contemplated that the describedimplementations may be included in or associated with a variety ofelectronic devices such as, but not limited to: mobile telephones,multimedia Internet enabled cellular telephones, mobile televisionreceivers, wireless devices, smartphones, smart cards, wearable devicessuch as bracelets, armbands, wristbands, rings, headbands, patches,etc., Bluetooth® devices, personal data assistants (PDAs), wirelesselectronic mail receivers, hand-held or portable computers, netbooks,notebooks, smartbooks, tablets, printers, copiers, scanners, facsimiledevices, global positioning system (GPS) receivers/navigators, cameras,digital media players (such as MP3 players), camcorders, game consoles,wrist watches, clocks, calculators, television monitors, flat paneldisplays, electronic reading devices (e.g., e-readers), mobile healthdevices, computer monitors, auto displays (including odometer andspeedometer displays, etc.), cockpit controls and/or displays, cameraview displays (such as the display of a rear view camera in a vehicle),electronic photographs, electronic billboards or signs, projectors,architectural structures, microwaves, refrigerators, stereo systems,cassette recorders or players, DVD players, CD players, VCRs, radios,portable memory chips, washers, dryers, washer/dryers, parking meters,packaging (such as in electromechanical systems (EMS) applicationsincluding microelectromechanical systems (MEMS) applications, as well asnon-EMS applications), aesthetic structures (such as display of imageson a piece of jewelry or clothing) and a variety of EMS devices. Theteachings herein also may be used in applications such as, but notlimited to, electronic switching devices, radio frequency filters,sensors, accelerometers, gyroscopes, motion-sensing devices,magnetometers, inertial components for consumer electronics, parts ofconsumer electronics products, steering wheels or other automobileparts, varactors, liquid crystal devices, electrophoretic devices, driveschemes, manufacturing processes and electronic test equipment. Thus,the teachings are not intended to be limited to the implementationsdepicted solely in the Figures, but instead have wide applicability aswill be readily apparent to one having ordinary skill in the art.

Various implementations disclosed herein may include a biometric systemthat is capable of optical excitation and ultrasonic imaging ofresultant acoustic wave generation. Such imaging may be referred toherein as “photoacoustic imaging.” Some such implementations may becapable of obtaining images from bones, muscle tissue, blood, bloodvessels, and/or other sub-epidermal features. As used herein, the term“sub-epidermal features” may refer to any of the tissue layers thatunderlie the epidermis, including the dermis, the subcutis, etc., andany blood vessels, lymph vessels, sweat glands, hair follicles, hairpapilla, fat lobules, etc., that may be present within such tissuelayers. Some implementations may be capable of biometric authenticationthat is based, at least in part, on image data obtained viaphotoacoustic imaging. In some examples, an authentication process maybe based on image data obtained via photoacoustic imaging and also onimage data obtained by transmitting ultrasonic waves and detectingcorresponding reflected ultrasonic waves.

In some implementations, the incident light wavelength or wavelengthsemitted by a light source system may be selected to trigger acousticwave emissions primarily from a particular type of material, such asblood, blood cells, blood vessels, blood vasculature, lymphaticvasculature, other soft tissue, or bones. The acoustic wave emissionsmay, in some examples, include ultrasonic waves. In some suchimplementations, the control system may be capable of estimating a bloodoxygen level, estimating a blood glucose level, or estimating both ablood oxygen level and a blood glucose level.

Alternatively, or additionally, the time interval between theirradiation time and the time during which resulting ultrasonic wavesare sampled (which may be referred to herein as the acquisition timedelay or the range-gate delay (RGD)) may be selected to receive acousticwave emissions primarily from a particular depth and/or from aparticular type of material. For example, a relatively larger range-gatedelay may be selected to receive acoustic wave emissions primarily frombones and a relatively smaller range-gate delay may be selected toreceive acoustic wave emissions primarily from sub-epidermal features(such as blood vessels, blood, etc.), muscle tissue features or bonetissue features.

Accordingly, some biometric systems disclosed herein may be capable ofacquiring images of sub-epidermal features via photoacoustic imaging. Insome implementations, a control system may be capable of acquiring firstultrasonic image data from acoustic wave emissions that are received byan ultrasonic sensor array during a first acquisition time window thatis initiated at an end time of a first acquisition time delay. Accordingto some examples, the control system may be capable of controlling adisplay to depict a two-dimensional (2-D) image that corresponds withthe first ultrasonic image data. In some instances, the control systemmay be capable of acquiring second through N^(th) ultrasonic image dataduring second through N^(th) acquisition time windows after secondthrough N^(th) acquisition time delays. Each of the second throughN^(th) acquisition time delays may correspond to a second through anN^(th) depth inside the target object. According to some examples, thecontrol system may be capable of controlling a display to depict athree-dimensional (3-D) image that corresponds with at least a subset ofthe first through N^(th) ultrasonic image data.

Particular implementations of the subject matter described in thisdisclosure can be implemented to realize one or more of the followingpotential advantages. Imaging sub-epidermal features (such as bloodvessels, blood, etc.), muscle tissue features, etc., using ultrasonictechnology alone can be challenging due to the small acoustic impedancecontrast between various types of soft tissue. In some photoacousticimaging implementations, a relatively higher signal-to-noise ratio maybe obtained for the resulting acoustic wave emission detection becausethe excitation is via optical stimulation instead of (or in addition to)ultrasonic wave transmission. The higher signal-to-noise ratio canprovide relatively more accurate and relatively more detailed imaging ofblood vessels and other sub-epidermal features. In addition to theinherent value of obtaining more detailed images (e.g., for improvedmedical determinations and diagnoses), the detailed imaging of bloodvessels and other sub-epidermal features can provide more reliable userauthentication and liveness determinations. Moreover, some photoacousticimaging implementations can detect changes in blood oxygen levels, whichcan provide enhanced liveness determinations. Some implementationsprovide a mobile device that includes a biometric system that is capableof some or all of the foregoing functionality. Some such mobile devicesmay be capable of displaying 2-D and/or 3-D images of sub-epidermalfeatures, bone tissue, etc.

FIG. 1 shows an example of components of blood being differentiallyheated by incident light and subsequently emitting acoustic waves. Inthis example, incident light 102 has been transmitted from a lightsource system (not shown) through a substrate 103 and into a bloodvessel 104 of an overlying finger 106. The surface of the finger 106includes ridges and valleys, so some of the incident light 102 has beentransmitted through the air 108 in this example. Here, the incidentlight 102 is causing optical excitation of illuminated blood and bloodcomponents in the blood vessel 104 and resultant acoustic wavegeneration. In this example, the generated acoustic waves 110 mayinclude ultrasonic waves.

In some implementations, such acoustic wave emissions may be detected bysensors of a sensor array, such as the ultrasonic sensor array 202 thatis described below with reference to FIG. 2. In some instances, theincident light wavelength, wavelengths and/or wavelength range(s) may beselected to trigger acoustic wave emissions primarily from a particulartype of material, such as blood, blood components, blood vessels, othersoft tissue, or bones.

FIG. 2 is a block diagram that shows example components of an apparatusaccording to some disclosed implementations. In this example, theapparatus 200 includes a biometric system. Here, the biometric systemincludes an ultrasonic sensor array 202, a light source system 204 and acontrol system 206. Although not shown in FIG. 2, the apparatus 200 mayinclude a substrate. Some examples are described below. Someimplementations of the apparatus 200 may include the optional ultrasonictransmitter 208.

Various examples of ultrasonic sensor arrays 202 are disclosed herein,some of which may include an ultrasonic transmitter and some of whichmay not. Although shown as separate elements in FIG. 2, in someimplementations the ultrasonic sensor array 202 and the ultrasonictransmitter 208 may be combined in an ultrasonic transceiver. Forexample, in some implementations, the ultrasonic sensor array 202 mayinclude a piezoelectric receiver layer, such as a layer of PVDF polymeror a layer of PVDF-TrFE copolymer. In some implementations, a separatepiezoelectric layer may serve as the ultrasonic transmitter. In someimplementations, a single piezoelectric layer may serve as thetransmitter and as a receiver. In some implementations, otherpiezoelectric materials may be used in the piezoelectric layer, such asaluminum nitride (AlN) or lead zirconate titanate (PZT). The ultrasonicsensor array 202 may, in some examples, include an array of ultrasonictransducer elements, such as an array of piezoelectric micromachinedultrasonic transducers (PMUTs), an array of capacitive micromachinedultrasonic transducers (CMUTs), etc. In some such examples, apiezoelectric receiver layer, PMUT elements in a single-layer array ofPMUTs, or CMUT elements in a single-layer array of CMUTs, may be used asultrasonic transmitters as well as ultrasonic receivers. According tosome alternative examples, the ultrasonic sensor array 202 may be anultrasonic receiver array and the ultrasonic transmitter 208 may includeone or more separate elements. In some such examples, the ultrasonictransmitter 208 may include an ultrasonic plane-wave generator, such asthose described below.

The light source system 204 may, in some examples, include an array oflight-emitting diodes. In some implementations, the light source system204 may include one or more laser diodes. According to someimplementations, the light source system may include at least oneinfrared, optical, red, green, blue, white or ultraviolet light-emittingdiode. In some implementations, the light source system 204 may includeone or more laser diodes. For example, the light source system 204 mayinclude at least one infrared, optical, red, green, blue or ultravioletlaser diode.

In some implementations, the light source system 204 may be capable ofemitting various wavelengths of light, which may be selectable totrigger acoustic wave emissions primarily from a particular type ofmaterial. For example, because the hemoglobin in blood absorbsnear-infrared light very strongly, in some implementations the lightsource system 204 may be capable of emitting one or more wavelengths oflight in the near-infrared range, in order to trigger acoustic waveemissions from hemoglobin. However, in some examples the control system206 may control the wavelength(s) of light emitted by the light sourcesystem 204 to preferentially induce acoustic waves in blood vessels,other soft tissue, and/or bones. For example, an infrared (IR)light-emitting diode LED may be selected and a short pulse of IR lightemitted to illuminate a portion of a target object and generate acousticwave emissions that are then detected by the ultrasonic sensor array202. In another example, an IR LED and a red LED or other color such asgreen, blue, white or ultraviolet (UV) may be selected and a short pulseof light emitted from each light source in turn with ultrasonic imagesobtained after light has been emitted from each light source. In otherimplementations, one or more light sources of different wavelengths maybe fired in turn or simultaneously to generate acoustic emissions thatmay be detected by the ultrasonic sensor array. Image data from theultrasonic sensor array that is obtained with light sources of differentwavelengths and at different depths (e.g., varying RGDs) into the targetobject may be combined to determine the location and type of material inthe target object. Image contrast may occur as materials in the bodygenerally absorb light at different wavelengths differently. Asmaterials in the body absorb light at a specific wavelength, they mayheat differentially and generate acoustic wave emissions withsufficiently short pulses of light having sufficient intensities. Depthcontrast may be obtained with light of different wavelengths and/orintensities at each selected wavelength. That is, successive images maybe obtained at a fixed RGD (which may correspond with a fixed depth intothe target object) with varying light intensities and wavelengths todetect materials and their locations within a target object. Forexample, hemoglobin, blood glucose or blood oxygen within a blood vesselinside a target object such as a finger may be detectedphotoacoustically.

According to some implementations, the light source system 204 may becapable of emitting a light pulse with a pulse width less than about 100nanoseconds. In some implementations, the light pulse may have a pulsewidth between about 10 nanoseconds and about 500 nanoseconds or more. Insome implementations, the light source system 204 may be capable ofemitting a plurality of light pulses at a pulse frequency between about1 MHz and about 100 MHz. In some examples, the pulse frequency of thelight pulses may correspond to an acoustic resonant frequency of theultrasonic sensor array and the substrate. For example, a set of four ormore light pulses may be emitted from the light source system 204 at afrequency that corresponds with the resonant frequency of a resonantacoustic cavity in the sensor stack, allowing a build-up of the receivedultrasonic waves and a higher resultant signal strength. In someimplementations, filtered light or light sources with specificwavelengths for detecting selected materials may be included with thelight source system 204. In some implementations, the light sourcesystem may contain light sources such as red, green and blue LEDs of adisplay that may be augmented with light sources of other wavelengths(such as IR and/or UV) and with light sources of higher optical power.For example, high-power laser diodes or electronic flash units (e.g., anLED or xenon flash unit) with or without filters may be used forshort-term illumination of the target object.

The control system 206 may include one or more general purpose single-or multi-chip processors, digital signal processors (DSPs), applicationspecific integrated circuits (ASICs), field programmable gate arrays(FPGAs) or other programmable logic devices, discrete gates ortransistor logic, discrete hardware components, or combinations thereof.The control system 206 also may include (and/or be configured forcommunication with) one or more memory devices, such as one or morerandom access memory (RAM) devices, read-only memory (ROM) devices, etc.Accordingly, the apparatus 200 may have a memory system that includesone or more memory devices, though the memory system is not shown inFIG. 2. The control system 206 may be capable of receiving andprocessing data from the ultrasonic sensor array 202, e.g., as describedbelow. If the apparatus 200 includes an ultrasonic transmitter 208, thecontrol system 206 may be capable of controlling the ultrasonictransmitter 208, e.g., as disclosed elsewhere herein. In someimplementations, functionality of the control system 206 may bepartitioned between one or more controllers or processors, such as adedicated sensor controller and an applications processor of a mobiledevice.

Although not shown in FIG. 2, some implementations of the apparatus 200may include an interface system. In some examples, the interface systemmay include a wireless interface system. In some implementations, theinterface system may include a user interface system, one or morenetwork interfaces, one or more interfaces between the control system206 and a memory system and/or one or more interfaces between thecontrol system 206 and one or more external device interfaces (e.g.,ports or applications processors).

The apparatus 200 may be used in a variety of different contexts, manyexamples of which are disclosed herein. For example, in someimplementations a mobile device may include the apparatus 200. In someimplementations, a wearable device may include the apparatus 200. Thewearable device may, for example, be a bracelet, an armband, awristband, a ring, a headband or a patch.

FIG. 3 is a flow diagram that provides examples of biometric systemoperations. The blocks of FIG. 3 (and those of other flow diagramsprovided herein) may, for example, be performed by the apparatus 200 ofFIG. 2 or by a similar apparatus. As with other methods disclosedherein, the method outlined in FIG. 3 may include more or fewer blocksthan indicated. Moreover, the blocks of methods disclosed herein are notnecessarily performed in the order indicated.

Here, block 305 involves controlling a light source system to emitlight. In some implementations, the control system 206 of the apparatus200 may control the light source system 204 to emit light. According tosome such implementations, the control system may be capable ofselecting one or more wavelengths of the light emitted by the lightsource system. In some implementations, the control system may becapable of selecting a light intensity associated with each selectedwavelength. For example, the control system may be capable of selectingthe one or more wavelengths of light and light intensities associatedwith each selected wavelength to generate acoustic wave emissions fromone or more portions of the target object. In some examples, the controlsystem may be capable of selecting the one or more wavelengths of lightto evaluate a one or more characteristics of the target object, e.g., toevaluate blood oxygen levels. Some examples are described below. In someexamples, block 305 may involve controlling a light source system toemit light that is transmitted through a substrate and/or other layersof an apparatus such as the apparatus 200.

According to this implementation, block 310 involves receiving signalsfrom an ultrasonic sensor array corresponding to acoustic waves emittedfrom portions of a target object in response to being illuminated withlight emitted by the light source system. In some instances the targetobject may be positioned on a surface of the ultrasonic sensor array orpositioned on a surface of a platen that is acoustically coupled to theultrasonic sensor array. The ultrasonic sensor array may, in someimplementations, be the ultrasonic sensor array 202 that is shown inFIG. 2 and described above. One or more coatings or acoustic matchinglayers may be included with the platen.

In some examples the target object may be a finger, as shown above inFIG. 1 and as described below with reference to FIG. 4. However, inother examples the target object may be another body part, such as apalm, a wrist, an arm, a leg, a torso, a head, etc. In some examples thetarget object may be a finger-like object that is being used in anattempt to spoof the apparatus 200, or another such apparatus, intoerroneously authenticating the finger-like object. For example, thefinger-like object may include silicone rubber, polyvinyl acetate (whiteglue), gelatin, glycerin, etc., with a fingerprint pattern formed on anoutside surface.

In some examples, the control system may be capable of selecting anacquisition time delay to receive acoustic wave emissions at acorresponding distance from the ultrasonic sensor array. Thecorresponding distance may correspond to a depth within the targetobject. According to some examples, the control system may be capable ofreceiving an acquisition time delay via a user interface, from a datastructure stored in memory, etc.

In some implementations, the control system may be capable of acquiringfirst ultrasonic image data from acoustic wave emissions that arereceived by an ultrasonic sensor array during a first acquisition timewindow that is initiated at an end time of a first acquisition timedelay. According to some examples, the control system may be capable ofcontrolling a display to depict a two-dimensional (2-D) image thatcorresponds with the first ultrasonic image data. In some instances, thecontrol system may be capable of acquiring second through N^(th)ultrasonic image data during second through N^(th) acquisition timewindows after second through N^(th) acquisition time delays. Each of thesecond through N^(th) acquisition time delays may correspond to secondthrough N^(th) depths inside the target object. According to someexamples, the control system may be capable of controlling a display todepict a reconstructed three-dimensional (3-D) image that correspondswith at least a subset of the first through N^(th) ultrasonic imagedata. Some examples are described below.

In this instance, block 315 involves performing a user authenticationprocess that is based, at least in part, on the signals from theultrasonic sensor array. Accordingly, in some examples, the userauthentication process may involve obtaining ultrasonic image data viaillumination of the target object with light emitted from the lightsource system. In some such examples, the ultrasonic image data obtainedvia illumination of the target object may include image datacorresponding to one or more sub-epidermal features, such as vascularimage data.

According to some such implementations, the user authentication processalso may involve obtaining ultrasonic image data via insonification ofthe target object with ultrasonic waves from an ultrasonic transmitter,such as the ultrasonic transmitter 208 shown in FIG. 2. In some suchexamples, the ultrasonic image data obtained via insonification of thetarget object may include fingerprint image data. However, in someimplementations the ultrasonic image data obtained via illumination ofthe target object and the ultrasonic image data obtained viainsonification of the target object may both be acquired primarily fromthe same depth inside the target object. In some examples, both theultrasonic image data obtained via illumination of the target object andthe ultrasonic image data obtained via insonification of the targetobject may be acquired from the same plurality of sensor pixels withinan ultrasonic sensor array.

The user authentication process may involve comparing “attributeinformation” obtained from received image data, based on the signalsfrom the ultrasonic sensor array, with stored attribute informationobtained from image data that has previously been received from anauthorized user during, for example, an enrollment process. In someexamples, the attribute information obtained from received image dataand the stored attribute information include attribute informationregarding subdermal features. According to some such examples, theattribute information may include information regarding subdermalfeatures, such as information regarding features of the dermis, featuresof the subcutis, blood vessel features, lymph vessel features, sweatgland features, hair follicle features, hair papilla features and/or fatlobule features.

Alternatively, or additionally, in some implementations the attributeinformation obtained from the received image data and the storedattribute information may include information regarding bone tissuefeatures, muscle tissue features and/or epidermal tissue features. Forexample, according to some implementations, the user authenticationprocess may involve controlling the ultrasonic transmitter to obtainfingerprint image data via the ultrasonic sensor array. In suchexamples, the authentication process may involve evaluating attributeinformation obtained from the fingerprint image data.

The attribute information obtained from the received image data and thestored attribute information that are compared during an authenticationprocess may include biometric template data corresponding to thereceived image data and biometric template data corresponding to thestored image data. One well-known type of biometric template data isfingerprint template data, which may indicate types and locations offingerprint minutia. A user authentication process based on attributesof fingerprint image data may involve comparing received and storedfingerprint template data. Such a process may or may not involvedirectly comparing received and stored fingerprint image data.

Similarly, biometric template data corresponding to subdermal featuresmay include information regarding the attributes of blood vessels, suchas information regarding the types and locations of blood vesselfeatures, such as blood vessel size, blood vessel orientation, thelocations of blood vessel branch points, etc. Alternatively, oradditionally, biometric template data corresponding to subdermalfeatures may include attribute information regarding the types (e.g.,the sizes, shapes, orientations, etc.) and locations of features of thedermis, features of the subcutis, lymph vessel features, sweat glandfeatures, hair follicle features, hair papilla features and/or fatlobule features.

Many spoofing techniques are based on forming fingerprint-like featureson an object, which may be a finger-like object. However, making afinger-like object with detailed subdermal features, muscle tissuefeatures and/or bone tissue features would be challenging and expensive.Making such features accurately correspond with those of an authorizeduser would be even more challenging. Because some disclosedimplementations involve obtaining attribute information that is based onsub-epidermal features, muscle tissue features and/or bone tissuefeatures, some such implementations may provide more reliableauthentication and may be capable of providing determinations of“liveness.” Some implementations described below, such as those capableof determining changes in blood oxygen and/or blood glucose levels, mayprovide enhanced liveness determinations.

FIG. 4 shows an example of a cross-sectional view of an apparatuscapable of performing the method of FIG. 3. The apparatus 400 is anexample of a device that may be included in a biometric system such asthose disclosed herein. Here, the apparatus 400 is an implementation ofthe apparatus 200 that is described above with reference to FIG. 2. Aswith other implementations shown and described herein, the types ofelements, the arrangement of the elements and the dimensions of theelements illustrated in FIG. 4 are merely shown by way of example.

FIG. 4 shows an example of a target object being illuminated by incidentlight and subsequently emitting acoustic waves. In this example, theapparatus 400 includes a light source system 204, which may include anarray of light-emitting diodes and/or an array of laser diodes. In someimplementations, the light source system 204 may be capable of emittingvarious wavelengths of light, which may be selectable to triggeracoustic wave emissions primarily from a particular type of material. Insome instances, the incident light wavelength, wavelengths and/orwavelength range(s) may be selected to trigger acoustic wave emissionsprimarily from a particular type of material, such as blood, bloodvessels, other soft tissue, or bones. To achieve sufficient imagecontrast, light sources 404 of the light source system 204 may need tohave a higher intensity and optical power output than light sourcesgenerally used to illuminate displays. In some implementations, lightsources with light output of 1-100 millijoules or more per pulse, withpulse widths of 100 nanoseconds or less, may be suitable. In someimplementations, light from an electronic flash unit such as thatassociated with a mobile device may be suitable. In someimplementations, the pulse width of the emitted light may be betweenabout 10 nanoseconds and about 500 nanoseconds or more.

In this example, incident light 102 has been transmitted from the lightsources 404 of the light system 204 through a sensor stack 405 and intoan overlying finger 106. The various layers of the sensor stack 405 mayinclude one or more substrates of glass or other material such asplastic or sapphire that is substantially transparent to the lightemitted by the light source system 204. In this example, the sensorstack 405 includes a substrate 410 to which the light source system 204is coupled, which may be a backlight of a display according to someimplementations. In alternative implementations, the light source system204 may be coupled to a front light. Accordingly, in someimplementations the light source system 204 may be configured forilluminating a display and the target object.

In this implementation, the substrate 410 is coupled to a thin-filmtransistor (TFT) substrate 415 for the ultrasonic sensor array 202.According to this example, a piezoelectric receiver layer 420 overliesthe sensor pixels 402 of the ultrasonic sensor array 202 and a platen425 overlies the piezoelectric receiver layer 420. Accordingly, in thisexample the apparatus 400 is capable of transmitting the incident light102 through one or more substrates of the sensor stack 405 that includethe ultrasonic sensor array 202 with substrate 415 and the platen 425that may also be viewed as a substrate. In some implementations, sensorpixels 402 of the ultrasonic sensor array 202 may be transparent,partially transparent or substantially transparent, such that theapparatus 400 may be capable of transmitting the incident light 102through elements of the ultrasonic sensor array 202. In someimplementations, the ultrasonic sensor array 202 and associatedcircuitry may be formed on or in a glass, plastic or silicon substrate.

In this example, the portion of the apparatus 400 that is shown in FIG.4 includes an ultrasonic sensor array 202 that is capable of functioningas an ultrasonic receiver. According to some implementations, theapparatus 400 may include an ultrasonic transmitter 208. The ultrasonictransmitter 208 may or may not be part of the ultrasonic sensor array202, depending on the particular implementation. In some examples, theultrasonic sensor array 202 may include PMUT or CMUT elements that arecapable of transmitting and receiving ultrasonic waves, and thepiezoelectric receiver layer 420 may be replaced with an acousticcoupling layer. In some examples, the ultrasonic sensor array 202 mayinclude an array of pixel input electrodes and sensor pixels formed inpart from TFT circuitry, an overlying piezoelectric receiver layer 420of piezoelectric material such as PVDF or PVDF-TrFE, and an upperelectrode layer positioned on the piezoelectric receiver layer sometimesreferred to as a receiver bias electrode. In the example shown in FIG.4, at least a portion of the apparatus 400 includes an ultrasonictransmitter 208 that can function as a plane-wave ultrasonictransmitter. The ultrasonic transmitter 208 may include a piezoelectrictransmitter layer with transmitter excitation electrodes disposed oneach side of the piezoelectric transmitter layer.

Here, the incident light 102 causes optical excitation within the finger106 and resultant acoustic wave generation. In this example, thegenerated acoustic waves 110 include ultrasonic waves. Acousticemissions generated by the absorption of incident light may be detectedby the ultrasonic sensor array 202. A high signal-to-noise ratio may beobtained because the resulting ultrasonic waves are caused by opticalstimulation instead of by reflection of transmitted ultrasonic waves.

FIG. 5 shows an example of a mobile device that includes a biometricsystem as disclosed herein. In this example, the mobile device 500 is asmart phone. However, in alternative examples the mobile device 500 mayanother type of mobile device, such as a mobile health device, awearable device, a tablet, etc.

In this example, the mobile device 500 includes an instance of theapparatus 200 that is described above with reference to FIG. 2. In thisexample, the apparatus 200 is disposed, at least in part, within themobile device enclosure 505. According to this example, at least aportion of the apparatus 200 is located in the portion of the mobiledevice 500 that is shown being touched by the finger 106, whichcorresponds to the location of button 510. Accordingly, the button 510may be an ultrasonic button. In some implementations, the button 510 mayserve as a home button. In some implementations, the button 510 mayserve as an ultrasonic authenticating button, with the ability to turnon or otherwise wake up the mobile device 500 when touched or pressedand/or to authenticate or otherwise validate a user when applicationsrunning on the mobile device (such as a wake-up function) warrant such afunction. Light sources for photoacoustic imaging may be included withinthe button 510.

In this implementation, the mobile device 500 may be capable ofperforming a user authentication process. For example, a control systemof the mobile device 500 may be capable of comparing attributeinformation obtained from image data received via an ultrasonic sensorarray of the apparatus 200 with stored attribute information obtainedfrom image data that has previously been received from an authorizeduser. In some examples, the attribute information obtained from thereceived image data and the stored attribute information may includeattribute information corresponding to at least one of sub-epidermalfeatures, muscle tissue features or bone tissue features.

According to some implementations, the attribute information obtainedfrom the received image data and the stored attribute information mayinclude information regarding fingerprint minutia. In some suchimplementations, the user authentication process may involve evaluatinginformation regarding the fingerprint minutia as well as at least oneother type of attribute information, such as attribute informationcorresponding to subdermal features. According to some such examples,the user authentication process may involve evaluating informationregarding the fingerprint minutia as well as attribute informationcorresponding to vascular features. For example, attribute informationobtained from a received image of blood vessels in the finger may becompared with a stored image of blood vessels in the authorized user'sfinger 106.

The apparatus 200 that is included in the mobile device 500 may or maynot include an ultrasonic transmitter, depending on the particularimplementation. However, in some examples, the user authenticationprocess may involve obtaining ultrasonic image data via insonificationof the target object with ultrasonic waves from an ultrasonictransmitter, as well as obtaining ultrasonic image data via illuminationof the target object with light emitted from the light source system.According to some such examples, the ultrasonic image data obtained viainsonification of the target object may include fingerprint image dataand the ultrasonic image data obtained via illumination of the targetobject may include vascular image data.

FIG. 6 is a flow diagram that provides further examples of biometricsystem operations. The blocks of FIG. 6 (and those of other flowdiagrams provided herein) may, for example, be performed by theapparatus 200 of FIG. 2 or by a similar apparatus. As with other methodsdisclosed herein, the method outlined in FIG. 6 may include more orfewer blocks than indicated. Moreover, the blocks of method 600, as wellas other methods disclosed herein, are not necessarily performed in theorder indicated.

Here, block 605 involves controlling a light source system to emitlight. In this example, the light may induce acoustic wave emissionsinside a target object in block 605. In some implementations, thecontrol system 206 of the apparatus 200 may control the light sourcesystem 204 to emit light in block 605. According to some suchimplementations, the control system 206 may be capable of controllingthe light source system 204 to emit at least one light pulse having aduration that is in the range of about 10 nanoseconds to about 500nanoseconds or more. For example, the control system 206 may be capableof controlling the light source system 204 to emit at least one lightpulse having a duration of approximately 10 nanoseconds, 20 nanoseconds,30 nanoseconds, 40 nanoseconds, 50 nanoseconds, 60 nanoseconds, 70nanoseconds, 80 nanoseconds, 90 nanoseconds, 100 nanoseconds, 120nanoseconds, 140 nanoseconds, 150 nanoseconds, 160 nanoseconds, 180nanoseconds, 200 nanoseconds, 300 nanoseconds, 400 nanoseconds, 500nanoseconds, etc. In some such implementations, the control system 206may be capable of controlling the light source system 204 to emit aplurality of light pulses at a frequency between about 1 MHz and about100 MHz. In other words, regardless of the wavelength(s) of light beingemitted by the light source system 204, the intervals between lightpulses may correspond to a frequency between about 1 MHz and about 100MHz or more. For example, the control system 206 may be capable ofcontrolling the light source system 204 to emit a plurality of lightpulses at a frequency of about 1 MHz, about 5 MHz, about 10 MHz, about15 MHz, about 20 MHz, about 25 MHz, about 30 MHz, about 40 MHz, about 50MHz, about 60 MHz, about 70 MHz, about 80 MHz, about 90 MHz, about 100MHz, etc. In some examples, light emitted by the light source system 204may be transmitted through an ultrasonic sensor array or through one ormore substrates of a sensor stack that includes an ultrasonic sensorarray.

According to this example, block 610 involves selecting a firstacquisition time delay to receive the acoustic wave emissions primarilyfrom a first depth inside the target object. In some such examples, thecontrol system may be capable of selecting an acquisition time delay toreceive acoustic wave emissions at a corresponding distance from theultrasonic sensor array. The corresponding distance may correspond to adepth within the target object. According to some such examples, theacquisition time delay may be measured from a time that the light sourcesystem emits light. In some examples, the acquisition time delay may bein the range of about 10 nanoseconds to over about 2000 nanoseconds.

According to some examples, a control system (such as the control system206) may be capable of selecting the first acquisition time delay. Insome examples, the control system may be capable of selecting theacquisition time delay based, at least on part, on user input. Forexample, the control system may be capable of receiving an indication oftarget depth or a distance from a platen surface of the biometric systemvia a user interface. The control system may be capable of determining acorresponding acquisition time delay from a data structure stored inmemory, by performing a calculation, etc. Accordingly, in some instancesthe control system's selection of an acquisition time delay may beaccording to user input and/or according to one or more acquisition timedelays stored in memory.

In this implementation, block 615 involves acquiring first ultrasonicimage data from the acoustic wave emissions received by an ultrasonicsensor array during a first acquisition time window that is initiated atan end time of the first acquisition time delay. Some implementationsmay involve controlling a display to depict a two-dimensional image thatcorresponds with the first ultrasonic image data. According to someimplementations, the first ultrasonic image data may be acquired duringthe first acquisition time window from a peak detector circuit disposedin each of a plurality of sensor pixels within the ultrasonic sensorarray. In some implementations, the peak detector circuitry may captureacoustic wave emissions or reflected ultrasonic wave signals during theacquisition time window. Some examples are described below withreference to FIG. 14.

In some examples, the first ultrasonic image data may include image datacorresponding to one or more sub-epidermal features, such as vascularimage data. According to some implementations, method 600 also mayinvolve obtaining second ultrasonic image data via insonification of thetarget object with ultrasonic waves from an ultrasonic transmitter. Insome such examples, the second ultrasonic image data may includefingerprint image data. However, in some implementations the firstultrasonic image data and the second ultrasonic image data may both beacquired primarily from the same depth inside the target object. In someexamples, both the first ultrasonic image data and the second ultrasonicimage data may be acquired from the same plurality of sensor pixelswithin an ultrasonic sensor array.

FIG. 7 shows examples of multiple acquisition time delays being selectedto receive acoustic waves emitted from different depths. In theseexamples, each of the acquisition time delays (which are labeledrange-gate delays or RGDs in FIG. 7) is measured from the beginning timet₁ of the photo-excitation signal 705 shown in graph 700. The graph 710depicts emitted acoustic waves (received wave (1) is one example) thatmay be received by an ultrasonic sensor array at an acquisition timedelay RGD₁ and sampled during an acquisition time window (also known asa range-gate window or a range-gate width) of RGW₁. Such acoustic waveswill generally be emitted from a relatively shallower portion of atarget object proximate, or positioned upon, a platen of the biometricsystem.

Graph 715 depicts emitted acoustic waves (received wave (2) is oneexample) that are received by the ultrasonic sensor array at anacquisition time delay RGD₂ (with RGD₂>RGD₁) and sampled during anacquisition time window of RGW₂. Such acoustic waves will generally beemitted from a relatively deeper portion of the target object. Graph 720depicts emitted acoustic waves (received wave (n) is one example) thatare received at an acquisition time delay RGD_(n) (withRGD_(n)>RGD₂>RGD₁) and sampled during an acquisition time window ofRGW_(n). Such acoustic waves will generally be emitted from a stilldeeper portion of the target object. Range-gate delays are typicallyinteger multiples of a clock period. A clock frequency of 128 MHz, forexample, has a clock period of 7.8125 nanoseconds, and RGDs may rangefrom under 10 nanoseconds to over 2000 nanoseconds. Similarly, therange-gate widths may also be integer multiples of the clock period, butare often much shorter than the RGD (e.g. less than about 50nanoseconds) to capture returning signals while retaining good axialresolution. In some implementations, the acquisition time window (e.g.RGW) may be between less than about 10 nanoseconds to about 200nanoseconds or more. Note that while various image bias levels (e.g. Txblock, Rx sample and Rx hold that may be applied to an Rx biaselectrode) may be in the single or low double-digit volt range, thereturn signals may have voltages in the tens or hundreds of millivolts.

FIG. 8 is a flow diagram that provides additional examples of biometricsystem operations. The blocks of FIG. 8 (and those of other flowdiagrams provided herein) may, for example, be performed by theapparatus 200 of FIG. 2 or by a similar apparatus. As with other methodsdisclosed herein, the method outlined in FIG. 8 may include more orfewer blocks than indicated. Moreover, the blocks of method 800, as wellas other methods disclosed herein, are not necessarily performed in theorder indicated.

Here, block 805 involves controlling a light source system to emitlight. In this example, the light may induce acoustic wave emissionsinside a target object in block 805. In some implementations, thecontrol system 206 of the apparatus 200 may control the light sourcesystem 204 to emit light in block 805. According to some suchimplementations, the control system 206 may be capable of controllingthe light source system 204 to emit at least one light pulse having aduration that is in the range of about 10 nanoseconds to about 500nanoseconds. In some such implementations, the control system 206 may becapable of controlling the light source system 204 to emit a pluralityof light pulses.

FIG. 9 shows examples of multiple acquisition time delays being selectedto receive ultrasonic waves emitted from different depths, in responseto a plurality of light pulses. In these examples, each of theacquisition time delays (which are labeled RGDs in FIG. 9) is measuredfrom the beginning time t₁ of the photo-excitation signal 905 a as shownin graph 900. Accordingly, the examples of FIG. 9 are similar to thoseof FIG. 7. However, in FIG. 9, the photo-excitation signal 905 a is onlythe first of multiple photo-excitation signals. In this example, themultiple photo-excitation signals include the photo-excitation signals905 b and 905 c, for a total of three photo-excitation signals. In otherimplementations, a control system may control a light source system toemit more or fewer photo-excitation signals. In some implementations,the control system may be capable of controlling the light source systemto emit a plurality of light pulses at a frequency between about 1 MHzand about 100 MHz.

The graph 910 illustrates ultrasonic waves (received wave packet (1) isone example) that are received by an ultrasonic sensor array at anacquisition time delay RGD₁ and sampled during an acquisition timewindow of RGW₁. Such ultrasonic waves will generally be emitted from arelatively shallower portion of a target object proximate to, orpositioned upon, a platen of the biometric system. By comparing receivedwave packet (1) with received wave (1) of FIG. 7, it may be seen thatthe received wave packet (1) has a relatively longer time duration and ahigher amplitude buildup than that of received wave (1) of FIG. 7. Thislonger time duration corresponds with the multiple photo-excitationsignals in the examples shown in FIG. 9, as compared to the singlephoto-excitation signal in the examples shown in FIG. 7.

Graph 915 illustrates ultrasonic waves (received wave packet (2) is oneexample) that are received by the ultrasonic sensor array at anacquisition time delay RGD₂ (with RGD₂>RGD₁) and sampled during anacquisition time window of RGW₂. Such ultrasonic waves will generally beemitted from a relatively deeper portion of the target object. Graph 920illustrates ultrasonic waves (received wave packet (n) is one example)that are received at an acquisition time delay RGD_(n) (withRGD_(n)>RGD₂>RGD₁) and sampled during an acquisition time window ofRGW_(n). Such ultrasonic waves will generally be emitted from stilldeeper portions of the target object.

Returning to FIG. 8, in this example block 810 involves selecting firstthrough N^(th) acquisition time delays to receive the acoustic waveemissions primarily from first through N^(th) depths inside the targetobject. In some such examples, the control system may be capable ofselecting the first through N^(th) acquisition time delays to receiveacoustic wave emissions at corresponding first through N^(th) distancesfrom the ultrasonic sensor array. The corresponding distances maycorrespond to first through N^(th) depths within the target object.According to some such examples, (e.g., as shown in FIGS. 7 and 9), theacquisition time delays may be measured from a time that the lightsource system emits light. In some examples, the first through N^(th)acquisition time delays may be in the range of about 10 nanoseconds toover about 2000 nanoseconds.

According to some examples, a control system (such as the control system206) may be capable of selecting the first through N^(th) acquisitiontime delays. In some examples, the control system may be capable ofreceiving one or more of the first through N^(th) acquisition timedelays (or one or more indications of depths or distances thatcorrespond to acquisition time delays) from a user interface, from adata structure stored in memory, or by calculation of one or moredepth-to-time conversions. Accordingly, in some instances the controlsystem's selection of the first through N^(th) acquisition time delaysmay be according to user input, according to one or more acquisitiontime delays stored in memory and/or according to a calculation.

In this implementation, block 815 involves acquiring first throughN^(th) ultrasonic image data from the acoustic wave emissions receivedby an ultrasonic sensor array during first through N^(th) acquisitiontime windows that are initiated at end times of the first through N^(th)acquisition time delays. According to some implementations, the firstthrough N^(th) ultrasonic image data may be acquired during firstthrough N^(th) acquisition time windows from a peak detector circuitdisposed in each of a plurality of sensor pixels within the ultrasonicsensor array.

In this example, block 820 involves processing the first through N^(th)ultrasonic image data. According to some implementations block 820 mayinvolve controlling a display to depict a two-dimensional image thatcorresponds with one of the first through N^(th) ultrasonic image data.In some implementations, block 820 may involve controlling a display todepict a reconstructed three-dimensional (3-D) image that correspondswith at least a subset of the first through N^(th) ultrasonic imagedata. Various examples are described below with reference to FIGS.10A-10F.

FIGS. 10A-10C are examples of cross-sectional views of a target objectpositioned on a platen of a biometric system such as those disclosedherein. In this example, the target object is a finger 106, which ispositioned on an outer surface of a platen 1005. FIGS. 10A-10C showexamples of tissues and structures of the finger 106, including theepidermis 1010, bone tissue 1015, blood vasculature 1020 and varioussub-epidermal tissues. In this example, incident light 102 has beentransmitted from a light source system (not shown) through the platen1005 and into the finger 106. Here, the incident light 102 has causedoptical excitation of the epidermis 1010 and blood vasculature 1020 andresultant generation of acoustic waves 110, which can be detected by theultrasonic sensor array 202.

FIGS. 10A-10C indicate ultrasonic image data being acquired at threedifferent range-gate delays (RGD₁, RGD₂ and RGD_(n)), which are alsoreferred to herein as acquisition time delays, after the beginning of atime interval of photo excitation. The dashed horizontal lines 1025 a,1025 b and 1025 n in FIGS. 10A-10C indicate the depth of eachcorresponding image. In some examples the photo excitation may be asingle pulse (e.g., as shown in FIG. 7), whereas in other examples thephoto excitation may include multiple pulses (e.g., as shown in FIG. 9).FIG. 10D is a cross-sectional view of the target object illustrated inFIGS. 10A-10C showing the image planes 1025 a, 1025 b, . . . 1025 n atvarying depths through which image data has been acquired.

FIG. 10E shows a series of simplified two-dimensional images thatcorrespond with ultrasonic image data acquired by the processes shown inFIGS. 10A-10C with reference to the image planes 1025 a, 1025 b and 1025n as shown in FIG. 10D. The two-dimensional images shown in FIG. 10Eprovide examples of two-dimensional images corresponding with ultrasonicimage data that a control system could, in some implementations, cause adisplay device to display.

Image₁ of FIG. 10E corresponds with the ultrasonic image data acquiredusing RGD₁, which corresponds with the depth 1025 a shown in FIGS. 10Aand 10D. Image′ includes a portion of the epidermis 1010 and bloodvasculature 1020 and also indicates structures of the sub-epidermaltissues.

Image₂ corresponds with ultrasonic image data acquired using RGD₂, whichcorresponds with the depth 1025 b shown in FIGS. 10B and 10D. Image₂also includes a portion of the epidermis 1010, blood vasculature 1020and indicates some additional structures of the sub-epidermal tissues.

Image_(n) corresponds with ultrasonic image data acquired using RGD_(n),which corresponds with the depth 1025 n shown in FIGS. 10C and 10D.Image_(n) includes a portion of the epidermis 1010, blood vasculature1020, some additional structures of the sub-epidermal tissues andstructures corresponding to bone tissue 1015. Image_(n) also includesstructures 1030 and 1032, which may correspond to bone tissue 1015and/or to connective tissue near the bone tissue 1015, such ascartilage. However, it is not clear from Image₁, Image₂ or Image_(n)what the structures of the blood vasculature 1020 and sub-epidermaltissues are or how they relate to one another.

These relationships may be more clearly seen the three-dimensional imageshown in FIG. 10F. FIG. 10F shows a composite of Image₁, Image₂ andImage_(n), as well as additional images corresponding to depths that arebetween depth 1025 b and depth 1025 n. A three-dimensional image may bemade from a set of two-dimensional images according to various methodsknown by those of skill in the art, such as a MATLAB® reconstructionroutine or other routine that enables reconstruction or estimations ofthree-dimensional structures from sets of two-dimensional layer data.These routines may use spline-fitting or other curve-fitting routinesand statistical techniques with interpolation to provide approximatecontours and shapes represented by the two-dimensional ultrasonic imagedata. As compared to the two-dimensional images shown in FIG. 10E, thethree-dimensional image shown in FIG. 10F more clearly representsstructures corresponding to bone tissue 1015 as well as sub-epidermalstructures including blood vasculature 1020, revealing vein, artery andcapillary structures and other vascular structures along with boneshape, size and features.

FIG. 11 shows an example of a mobile device that includes a biometricsystem capable of performing methods disclosed herein. A mobile devicethat includes such a biometric system may be capable of various types ofmobile health monitoring, such as the imaging of blood vessel patterns,the analysis of blood and tissue components, etc.

In this example, the mobile device 1100 includes an instance of theapparatus 200 that is capable of functioning as an in-displayphotoacoustic imager (PAI). The apparatus 200 may, for example, becapable of emitting light that induces acoustic wave emissions inside atarget object and acquiring ultrasonic image data from acoustic waveemissions received by an ultrasonic sensor array. In some examples, theapparatus 200 may be capable of acquiring ultrasonic image data duringone or more acquisition time windows that are initiated at the end timeof one or more acquisition time delays.

According to some implementations, the mobile device 1100 may be capableof displaying two-dimensional and/or three-dimensional images on thedisplay 1105 that correspond with ultrasonic image data obtained via theapparatus 200. In other implementations, the mobile device may transmitultrasonic image data (and/or attributes obtained from ultrasonic imagedata) to another device for processing and/or display.

In some examples, a control system of the mobile device 1100 (which mayinclude a control system of the apparatus 200) may be capable ofselecting one or more wavelengths of the light emitted by the apparatus200. In some examples, the control system may be capable of selectingone or more wavelengths of light to trigger acoustic wave emissionsprimarily from a particular type of material in the target object.According to some implementations, the control system may be capable ofestimating a blood oxygen level and/or of estimating a blood glucoselevel. In some implementations, the control system may be capable ofselecting one or more wavelengths of light according to user input. Forexample, the mobile device 1100 may allow a user or a specializedsoftware application to enter values corresponding to one or morewavelengths of the light emitted by the apparatus 200. Alternatively, oradditionally, the mobile device 1100 may allow a user to select adesired function (such as estimating a blood oxygen level) and maydetermine one or more corresponding wavelengths of light to be emittedby the apparatus 200. For example, in some implementations, a wavelengthin the mid-infrared region of the electromagnetic spectrum may beselected and a set of ultrasonic image data may be acquired in thevicinity of blood inside a blood vessel within a target object such as afinger or wrist. A second wavelength in another portion of the infraredregion (e.g. near IR region) or in a visible region such as a redwavelength may be selected and a second set of ultrasonic image data maybe acquired in the same vicinity as the first ultrasonic image data. Acomparison of the first and second sets of ultrasonic image data, inconjunction with image data from other wavelengths or combinations ofwavelengths, may allow an estimation of the blood glucose levels and/orblood oxygen levels within the target object.

In some implementations, a light source system of the mobile device 1100may include at least one backlight or front light configured forilluminating the display 1105 and a target object. For example, thelight source system may include one or more laser diodes, semiconductorlasers or light-emitting diodes. In some examples, the light sourcesystem may include at least one infrared, optical, red, green, blue,white or ultraviolet light-emitting diode or at least one infrared,optical, red, green, blue or ultraviolet laser diode. According to someimplementations, the control system may be capable of controlling thelight source system to emit at least one light pulse having a durationthat is in the range of about 10 nanoseconds to about 500 nanoseconds.In some instances, the control system may be capable of controlling thelight source system to emit a plurality of light pulses at a frequencybetween about 1 MHz and about 100 MHz.

In this example, the mobile device 1100 may include an ultrasonicauthenticating button 1110 that includes another instance of theapparatus 200 that is capable of performing a user authenticationprocess. In some such examples, the ultrasonic authenticating button1110 may include an ultrasonic transmitter. According to some examples,the user authentication process may involve obtaining ultrasonic imagedata via insonification of a target object with ultrasonic waves from anultrasonic transmitter and obtaining ultrasonic image data viaillumination of the target object with light emitted from the lightsource system. In some such implementations, the ultrasonic image dataobtained via insonification of the target object may include fingerprintimage data and the ultrasonic image data obtained via illumination ofthe target object may include image data corresponding to one or moresub-epidermal features, such as vascular image data.

In this implementation, both the display 1105 and the apparatus 200 areon the side of the mobile device that is facing a target object, whichis a wrist in this example, which may be imaged via the apparatus 200.However, in alternative implementations, the apparatus 200 may be on theopposite side of the mobile device 1100. For example, the display 1105may be on the front of the mobile device and the apparatus 200 may be onthe back of the mobile device. According to some such implementations,the mobile device may be capable of displaying two-dimensional and/orthree-dimensional images, analogous to those shown in FIGS. 10E and 10F,as the corresponding ultrasonic image data are being acquired.

In some implementations, a portion of a target object, such as a wristor arm, may be scanned as the mobile device 1100 is moved. According tosome such implementations, a control system of the mobile device 1100may be capable of stitching together the scanned images to form a morecomplete and larger two-dimensional or three-dimensional image. In someexamples, the control system may be capable of acquiring first andsecond ultrasonic image data at primarily a first depth inside a targetobject. The second ultrasonic image data may be acquired after thetarget object or the mobile device 1100 is repositioned. In someimplementations, the second ultrasonic image data may be acquired aftera period of time corresponding to a frame rate, such as a frame ratebetween about one frame per second and about thirty frames per second ormore. According to some such examples, the control system may be capableof stitching together or otherwise assembling the first and secondultrasonic image data to form a composite ultrasonic image.

FIG. 12 is a flow diagram that provides an example of a method ofstitching ultrasonic image data obtained via a mobile device such asthat shown in FIG. 11. As with other methods disclosed herein, themethod outlined in FIG. 12 may include more or fewer blocks thanindicated. Moreover, the blocks of method 1200 are not necessarilyperformed in the order indicated.

Here, block 1205 involves receiving an indication to obtain stitchedultrasonic images via a mobile device. In this example, block 1205involves receiving an indication to obtain stitched two-dimensionalultrasonic images. In alternative examples, block 1205 may involvereceiving an indication to obtain stitched three-dimensional ultrasonicimages. For example, a software application running on a mobile devicemay recognize that a larger view of an area of interest within a targetobject is desired after receiving an answer to a prompt provided to auser, and provide an indication to stitch or otherwise assemble acollection of two-dimensional or three-dimensional images obtained asthe mobile device is moved over and around the area of interest.

In this example, block 1210 involves receiving an indication of a firstacquisition time delay. Block 1205 and/or block 1210 may, for example,involve receiving input from a user interface system, e.g., in responseto user interaction with a graphical user interface via touch screen, inresponse to user interaction with a button, etc. In someimplementations, the acquisition time delay may correspond with adistance from an ultrasonic sensor array of the mobile device and/or toa depth within a target object. Accordingly, the user input maycorrespond to time, distance, depth or another appropriate metric. Inalternative examples wherein block 1205 involves receiving an indicationto obtain stitched three-dimensional ultrasonic images, block 1210 mayinvolve receiving an indication of first through N^(th) acquisition timedelays. According to some examples, a control system of the mobiledevice may receive one or more acquisition time delays from a userinterface, from a data structure stored in memory, etc., in block 1210.

In this example, block 1215 involves controlling a light source systemof the mobile device to emit light at a current position of the mobiledevice. In this example, the light induces acoustic wave emissionsinside a target object. According to this implementation, block 1220involves acquiring, at the current position, ultrasonic image data fromthe acoustic wave emissions. In this implementation, the acoustic waveemissions are received by an ultrasonic sensor array of the mobile atthe current position of the mobile device during a first acquisitiontime window that is initiated at an end time of the first acquisitiontime delay. In alternative examples wherein block 1205 involvesreceiving an indication to obtain stitched three-dimensional ultrasonicimages, block 1220 may involve acquiring, at the current position,ultrasonic image data during first through N^(th) acquisition timewindows after corresponding first through N^(th) acquisition timedelays.

In this implementation, block 1225 involves processing the acquiredultrasonic image data. In some examples, block 1225 may involvedisplaying the acquired ultrasonic image data. According to someimplementations, block 1225 may involve identifying distinctive featuresof the acquired ultrasonic image data. Such distinctive features may beused for aligning the ultrasonic image data acquired in block 1220 withpreviously-acquired or subsequently-acquired ultrasonic image data froman overlapping area of the target object. Such distinctive features maybe used during further processes of image stitching, e.g., as describedbelow.

In this example, block 1230 involves receiving an indication that themobile device has changed position. For example, block 1230 may involvereceiving inertial sensor data from an inertial sensor system of themobile device, such as sensor data from one or more accelerometers orangular rate sensors (e.g. gyroscopes) within the mobile device. Basedon the inertial sensor data, a control system of the mobile device maydetermine that the mobile device has changed position. In someimplementations, image data from a front-facing or rear-facing cameramay be used to detect that the mobile device has changed position. Insome implementations, a user may be prompted to provide an indicationwhen the mobile device has changed positioned, for example, by pressingor otherwise touching an image-capture button.

In block 1235, it is determined whether to continue obtaining ultrasonicimage data. In some instances, block 1235 may involve receiving anindication from a user interface system to stop obtaining ultrasonicimage data. In some instances, block 1235 may involve receiving anindication as to whether a predetermined time interval for obtainingultrasonic image data has elapsed.

If it is determined to continue obtaining ultrasonic image data in block1235, in this example the process reverts to block 1215 and the lightsource system emits light at the current position of the mobile device.The process then continues to block 1220 and additional ultrasonic imagedata are acquired, at the current position, during the first acquisitiontime window that is initiated at the end time of the first acquisitiontime delay.

The process then continues to block 1225, in which at least theadditional ultrasonic image data are processed. In some examples, atleast the additional ultrasonic image data may be displayed. Accordingto some implementations, block 1225 may involve identifying distinctivefeatures of the additional ultrasonic image data. In some suchimplementations, the distinctive features may be used for aligning theadditional ultrasonic image data acquired in block 1220 withpreviously-acquired or subsequently-acquired ultrasonic image data froman overlapping area of the target object.

Since at least two instances of ultrasonic image data will have beenacquired after two iterations of blocks 1215 and 1220, block 1225 mayinvolve a registration process for image stitching. In someimplementations, the registration process may involve a search for imagealignments that minimize the sum of absolute differences between valuesof overlapping image pixels. In some examples, the registration processmay involve a random sample consensus (RANSAC) method. In some examples,block 1225 may involve an image alignment process. In some suchimplementations, block 1225 may involve a compositing process, duringwhich images are aligned such that they appear as a single compositeimage. According to some implementations, block 1225 may involve animage blending process. For example, block 1225 may involve motioncompensation, seam line adjustment to minimize the visibility of seamsbetween adjacent images, etc.

In this implementation, method 1200 continues until it is determined inblock 1235 not to continue obtaining ultrasonic image data, at whichpoint the process ends. However, some implementations may involveadditional operations after it is determined in block 1235 not tocontinue obtaining ultrasonic image data. In some such implementations,stitched ultrasonic image data may be displayed, stored in a memoryand/or transmitted to another device.

FIG. 13 is a flow diagram that shows blocks of a method of oxidizedhemoglobin detection that may be performed with some disclosed biometricsystems. As with other methods disclosed herein, the method outlined inFIG. 13 may include more or fewer blocks than indicated. Moreover, theblocks of method 1300 are not necessarily performed in the orderindicated.

Here, block 1305 involves receiving an indication that a target object(such as a finger, palm or wrist) is positioned proximate a biometricsystem that includes an ultrasonic sensor array and a light sourcesystem. For example, block 1305 may involve receiving an indication thatthe target object is positioned on a platen of the biometric system. Insome implementations, an application running on a mobile device having abiometric system with photoacoustic imaging capability may cue a user totouch or press a button to indicate when the target object is positionedon the platen. In some implementations, the biometric system may senseultrasonically or capacitively when the target object is in contact withthe platen surface and provide the indication accordingly.

In this implementation, block 1310 involves selecting an acquisitiontime delay. For example, block 1310 may involve selecting an acquisitiontime delay according to user input received from a user interfacesystem. The acquisition time delay may correspond with a target ofinterest, such as blood in a blood vessel in this example. In someimplementations, block 1310 also may involve selecting a firstwavelength of light and a second wavelength of light and a lightintensity associated with each selected wavelength for illuminating thetarget object. According to some implementations, block 1310 may involveselecting one or more wavelengths of light according to user inputregarding a desired type of functionality, such as oxidized hemoglobindetection, estimating a blood glucose level, etc.

According to this example, block 1315 involves illuminating the targetobject with light of the first wavelength. For example, block 1315 mayinvolve illuminating the target object with near-infrared light, whichis strongly absorbed by oxygenated hemoglobin.

Here, block 1320 involves acquiring first ultrasonic image data at theselected acquisition time delay. In this example, the first ultrasonicimage data corresponds to acoustic waves that were induced byilluminating the target object with light of the first wavelength, suchas near-infrared light.

In this example, block 1325 involves illuminating the target object withlight of the second wavelength. For example, instead of illuminating thetarget object with near-infrared light, block 1325 may involveilluminating the target object with a different wavelength of light,such as light in the visible range. Light in the visible range, such asred or green light, is not strongly absorbed by oxygenated hemoglobin,but instead tends to be transmitted.

According to this implementation, block 1330 involves acquiring secondultrasonic image data at the selected acquisition time delay. In thisexample, the second ultrasonic image data correspond to acoustic wavesthat were induced by illuminating the target object with light of thesecond wavelength, such as red or green light. By comparing the firstultrasonic image data with the second ultrasonic image data, bloodoxygen levels may be estimated. For example, with appropriatecalibration coefficients, the signal levels from the first ultrasonicimage data may be normalized by the signal levels from the secondultrasonic image data in a region of interest such as within a bloodvessel and the ratio compared to a stored table of values that convertsthe normalized data into, for example, blood oxygen level as apercentage of oxygen saturation (e.g. SO₂), as a percentage ofperipheral oxygen saturation (e.g. SpO₂) or as a percentage of arterialoxygen saturation (e.g. SaO₂).

FIG. 14 representationally depicts aspects of a 4×4 pixel array 1435 ofsensor pixels 1434 for an ultrasonic sensor system. Each pixel 1434 maybe, for example, associated with a local region of piezoelectric sensormaterial (PSM), a peak detection diode (D1) and a readout transistor(M3); many or all of these elements may be formed on or in a substrateto form the pixel circuit 1436. In practice, the local region ofpiezoelectric sensor material of each pixel 1434 may transduce receivedultrasonic energy into electrical charges. The peak detection diode D1may register the maximum amount of charge detected by the local regionof piezoelectric sensor material PSM. Each row of the pixel array 1435may then be scanned, e.g., through a row select mechanism, a gatedriver, or a shift register, and the readout transistor M3 for eachcolumn may be triggered to allow the magnitude of the peak charge foreach pixel 1434 to be read by additional circuitry, e.g., a multiplexerand an A/D converter. The pixel circuit 1436 may include one or moreTFTs to allow gating, addressing, and resetting of the pixel 1434.

Each pixel circuit 1436 may provide information about a small portion ofthe object detected by the ultrasonic sensor system. While, forconvenience of illustration, the example shown in FIG. 14 is of arelatively coarse resolution, ultrasonic sensors having a resolution onthe order of 500 pixels per inch or higher may be configured with anappropriately scaled structure. The detection area of the ultrasonicsensor system may be selected depending on the intended object ofdetection. For example, the detection area may range from about 5 mm×5mm for a single finger to about 3 inches×3 inches for four fingers.Smaller and larger areas, including square, rectangular andnon-rectangular geometries, may be used as appropriate for the targetobject.

FIG. 15A shows an example of an exploded view of an ultrasonic sensorsystem. In this example, the ultrasonic sensor system 1500 a includes anultrasonic transmitter 20 and an ultrasonic receiver 30 under a platen40. According to some implementations, the ultrasonic receiver 30 may bean example of the ultrasonic sensor array 202 that is shown in FIG. 2and described above. In some implementations, the ultrasonic transmitter20 may be an example of the optional ultrasonic transmitter 208 that isshown in FIG. 2 and described above. The ultrasonic transmitter 20 mayinclude a substantially planar piezoelectric transmitter layer 22 andmay be capable of functioning as a plane wave generator. Ultrasonicwaves may be generated by applying a voltage to the piezoelectric layerto expand or contract the layer, depending upon the signal applied,thereby generating a plane wave. In this example, the control system 206may be capable of causing a voltage that may be applied to the planarpiezoelectric transmitter layer 22 via a first transmitter electrode 24and a second transmitter electrode 26, In this fashion, an ultrasonicwave may be made by changing the thickness of the layer via apiezoelectric effect. This ultrasonic wave may travel towards a finger(or other object to be detected), passing through the platen 40. Aportion of the wave not absorbed or transmitted by the object to bedetected may be reflected so as to pass back through the platen 40 andbe received by the ultrasonic receiver 30. The first and secondtransmitter electrodes 24 and 26 may be metallized electrodes, forexample, metal layers that coat opposing sides of the piezoelectrictransmitter layer 22.

The ultrasonic receiver 30 may include an array of sensor pixel circuits32 disposed on a substrate 34, which also may be referred to as abackplane, and a piezoelectric receiver layer 36. In someimplementations, each sensor pixel circuit 32 may include one or moreTFT elements, electrical interconnect traces and, in someimplementations, one or more additional circuit elements such as diodes,capacitors, and the like. Each sensor pixel circuit 32 may be configuredto convert an electric charge generated in the piezoelectric receiverlayer 36 proximate to the pixel circuit into an electrical signal. Eachsensor pixel circuit 32 may include a pixel input electrode 38 thatelectrically couples the piezoelectric receiver layer 36 to the sensorpixel circuit 32.

In the illustrated implementation, a receiver bias electrode 39 isdisposed on a side of the piezoelectric receiver layer 36 proximal toplaten 40. The receiver bias electrode 39 may be a metallized electrodeand may be grounded or biased to control which signals may be passed tothe array of sensor pixel circuits 32. Ultrasonic energy that isreflected from the exposed (top) surface of the platen 40 may beconverted into localized electrical charges by the piezoelectricreceiver layer 36. These localized charges may be collected by the pixelinput electrodes 38 and passed on to the underlying sensor pixelcircuits 32. The charges may be amplified or buffered by the sensorpixel circuits 32 and provided to the control system 206.

The control system 206 may be electrically connected (directly orindirectly) with the first transmitter electrode 24 and the secondtransmitter electrode 26, as well as with the receiver bias electrode 39and the sensor pixel circuits 32 on the substrate 34. In someimplementations, the control system 206 may operate substantially asdescribed above. For example, the control system 206 may be capable ofprocessing the amplified signals received from the sensor pixel circuits32.

The control system 206 may be capable of controlling the ultrasonictransmitter 20 and/or the ultrasonic receiver 30 to obtain ultrasonicimage data, e.g., by obtaining fingerprint images. Whether or not theultrasonic sensor system 1500 a includes an ultrasonic transmitter 20,the control system 206 may be capable of obtaining attribute informationfrom the ultrasonic image data. In some examples, the control system 206may be capable of controlling access to one or more devices based, atleast in part, on the attribute information. The ultrasonic sensorsystem 1500 a (or an associated device) may include a memory system thatincludes one or more memory devices. In some implementations, thecontrol system 206 may include at least a portion of the memory system.The control system 206 may be capable of obtaining attribute informationfrom ultrasonic image data and storing the attribute information in thememory system. In some implementations, the control system 206 may becapable of capturing a fingerprint image, obtaining attributeinformation from the fingerprint image and storing attribute informationobtained from the fingerprint image (which may be referred to herein asfingerprint image information) in the memory system. According to someexamples, the control system 206 may be capable of capturing afingerprint image, obtaining attribute information from the fingerprintimage and storing attribute information obtained from the fingerprintimage even while maintaining the ultrasonic transmitter 20 in an “off”state.

In some implementations, the control system 206 may be capable ofoperating the ultrasonic sensor system 1500 a in an ultrasonic imagingmode or a force-sensing mode. In some implementations, the controlsystem may be capable of maintaining the ultrasonic transmitter 20 in an“off” state when operating the ultrasonic sensor system in aforce-sensing mode. The ultrasonic receiver 30 may be capable offunctioning as a force sensor when the ultrasonic sensor system 1500 ais operating in the force-sensing mode. In some implementations, thecontrol system 206 may be capable of controlling other devices, such asa display system, a communication system, etc. In some implementations,the control system 206 may be capable of operating the ultrasonic sensorsystem 1500 a in a capacitive imaging mode.

The platen 40 may be any appropriate material that can be acousticallycoupled to the receiver, with examples including plastic, ceramic,sapphire, metal and glass. In some implementations, the platen 40 may bea cover plate, e.g., a cover glass or a lens glass for a display.Particularly when the ultrasonic transmitter 20 is in use, fingerprintdetection and imaging can be performed through relatively thick platensif desired, e.g., 3 mm and above. However, for implementations in whichthe ultrasonic receiver 30 is capable of imaging fingerprints in a forcedetection mode or a capacitance detection mode, a thinner and relativelymore compliant platen 40 may be desirable. According to some suchimplementations, the platen 40 may include one or more polymers, such asone or more types of parylene, and may be substantially thinner. In somesuch implementations, the platen 40 may be tens of microns thick or evenless than 10 microns thick.

Examples of piezoelectric materials that may be used to form thepiezoelectric receiver layer 36 include piezoelectric polymers havingappropriate acoustic properties, for example, an acoustic impedancebetween about 2.5 MRayls and 5 MRayls. Specific examples ofpiezoelectric materials that may be employed include ferroelectricpolymers such as polyvinylidene fluoride (PVDF) and polyvinylidenefluoride-trifluoroethylene (PVDF-TrFE) copolymers. Examples of PVDFcopolymers include 60:40 (molar percent) PVDF-TrFE, 70:30 PVDF-TrFE,80:20 PVDF-TrFE, and 90:10 PVDR-TrFE. Other examples of piezoelectricmaterials that may be employed include polyvinylidene chloride (PVDC)homopolymers and copolymers, polytetrafluoroethylene (PTFE) homopolymersand copolymers, and diisopropylammonium bromide (DIPAB).

The thickness of each of the piezoelectric transmitter layer 22 and thepiezoelectric receiver layer 36 may be selected so as to be suitable forgenerating and receiving ultrasonic waves. In one example, a PVDF planarpiezoelectric transmitter layer 22 is approximately 28 μm thick and aPVDF-TrFE receiver layer 36 is approximately 12 μm thick. Examplefrequencies of the ultrasonic waves may be in the range of 5 MHz to 30MHz, with wavelengths on the order of a millimeter or less.

FIG. 15B shows an exploded view of an alternative example of anultrasonic sensor system. In this example, the piezoelectric receiverlayer 36 has been formed into discrete elements 37. In theimplementation shown in FIG. 15B, each of the discrete elements 37corresponds with a single pixel input electrode 38 and a single sensorpixel circuit 32. However, in alternative implementations of theultrasonic sensor system 1500 b, there is not necessarily a one-to-onecorrespondence between each of the discrete elements 37, a single pixelinput electrode 38 and a single sensor pixel circuit 32. For example, insome implementations there may be multiple pixel input electrodes 38 andsensor pixel circuits 32 for a single discrete element 37.

FIGS. 15A and 15B show example arrangements of ultrasonic transmittersand receivers in an ultrasonic sensor system, with other arrangementspossible. For example, in some implementations, the ultrasonictransmitter 20 may be above the ultrasonic receiver 30 and thereforecloser to the object(s) 25 to be detected. In some implementations, theultrasonic transmitter may be included with the ultrasonic sensor array(e.g., a single-layer transmitter and receiver). In someimplementations, the ultrasonic sensor system may include an acousticdelay layer. For example, an acoustic delay layer may be incorporatedinto the ultrasonic sensor system between the ultrasonic transmitter 20and the ultrasonic receiver 30. An acoustic delay layer may be employedto adjust the ultrasonic pulse timing, and at the same time electricallyinsulate the ultrasonic receiver 30 from the ultrasonic transmitter 20.The acoustic delay layer may have a substantially uniform thickness,with the material used for the delay layer and/or the thickness of thedelay layer selected to provide a desired delay in the time forreflected ultrasonic energy to reach the ultrasonic receiver 30. Indoing so, the range of time during which an energy pulse that carriesinformation about the object by virtue of having been reflected by theobject may be made to arrive at the ultrasonic receiver 30 during a timerange when it is unlikely that energy reflected from other parts of theultrasonic sensor system is arriving at the ultrasonic receiver 30. Insome implementations, the substrate 34 and/or the platen 40 may serve asan acoustic delay layer.

As used herein, a phrase referring to “at least one of” a list of itemsrefers to any combination of those items, including single members. Asan example, “at least one of: a, b, or c” is intended to cover: a, b, c,a-b, a-c, b-c, and a-b-c.

The various illustrative logics, logical blocks, modules, circuits andalgorithm processes described in connection with the implementationsdisclosed herein may be implemented as electronic hardware, computersoftware, or combinations of both. The interchangeability of hardwareand software has been described generally, in terms of functionality,and illustrated in the various illustrative components, blocks, modules,circuits and processes described above. Whether such functionality isimplemented in hardware or software depends upon the particularapplication and design constraints imposed on the overall system.

The hardware and data processing apparatus used to implement the variousillustrative logics, logical blocks, modules and circuits described inconnection with the aspects disclosed herein may be implemented orperformed with a general purpose single- or multi-chip processor, adigital signal processor (DSP), an application specific integratedcircuit (ASIC), a field programmable gate array (FPGA) or otherprogrammable logic device, discrete gate or transistor logic, discretehardware components, or any combination thereof designed to perform thefunctions described herein. A general purpose processor may be amicroprocessor, or, any conventional processor, controller,microcontroller, or state machine. A processor also may be implementedas a combination of computing devices, e.g., a combination of a DSP anda microprocessor, a plurality of microprocessors, one or moremicroprocessors in conjunction with a DSP core, or any other suchconfiguration. In some implementations, particular processes and methodsmay be performed by circuitry that is specific to a given function.

In one or more aspects, the functions described may be implemented inhardware, digital electronic circuitry, computer software, firmware,including the structures disclosed in this specification and theirstructural equivalents thereof, or in any combination thereof.Implementations of the subject matter described in this specificationalso may be implemented as one or more computer programs, i.e., one ormore modules of computer program instructions, encoded on a computerstorage media for execution by, or to control the operation of, dataprocessing apparatus.

If implemented in software, the functions may be stored on ortransmitted over as one or more instructions or code on acomputer-readable medium, such as a non-transitory medium. The processesof a method or algorithm disclosed herein may be implemented in aprocessor-executable software module which may reside on acomputer-readable medium. Computer-readable media include both computerstorage media and communication media including any medium that may beenabled to transfer a computer program from one place to another.Storage media may be any available media that may be accessed by acomputer. By way of example, and not limitation, non-transitory mediamay include RAM, ROM, EEPROM, CD-ROM or other optical disk storage,magnetic disk storage or other magnetic storage devices, or any othermedium that may be used to store desired program code in the form ofinstructions or data structures and that may be accessed by a computer.Also, any connection may be properly termed a computer-readable medium.Disk and disc, as used herein, includes compact disc (CD), laser disc,optical disc, digital versatile disc (DVD), floppy disk, and blu-raydisc where disks usually reproduce data magnetically, while discsreproduce data optically with lasers. Combinations of the above shouldalso be included within the scope of computer-readable media.Additionally, the operations of a method or algorithm may reside as oneor any combination or set of codes and instructions on a machinereadable medium and computer-readable medium, which may be incorporatedinto a computer program product.

Various modifications to the implementations described in thisdisclosure may be readily apparent to those having ordinary skill in theart, and the generic principles defined herein may be applied to otherimplementations without departing from the spirit or scope of thisdisclosure. Thus, the disclosure is not intended to be limited to theimplementations shown herein, but is to be accorded the widest scopeconsistent with the claims, the principles and the novel featuresdisclosed herein. The word “exemplary” is used exclusively herein, if atall, to mean “serving as an example, instance, or illustration.” Anyimplementation described herein as “exemplary” is not necessarily to beconstrued as preferred or advantageous over other implementations.

Certain features that are described in this specification in the contextof separate implementations also may be implemented in combination in asingle implementation. Conversely, various features that are describedin the context of a single implementation also may be implemented inmultiple implementations separately or in any suitable subcombination.Moreover, although features may be described above as acting in certaincombinations and even initially claimed as such, one or more featuresfrom a claimed combination may in some cases be excised from thecombination, and the claimed combination may be directed to asubcombination or variation of a sub combination.

Similarly, while operations are depicted in the drawings in a particularorder, this should not be understood as requiring that such operationsbe performed in the particular order shown or in sequential order, orthat all illustrated operations be performed, to achieve desirableresults. In certain circumstances, multitasking and parallel processingmay be advantageous. Moreover, the separation of various systemcomponents in the implementations described above should not beunderstood as requiring such separation in all implementations, and itshould be understood that the described program components and systemsmay generally be integrated together in a single software product orpackaged into multiple software products. Additionally, otherimplementations are within the scope of the following claims. In somecases, the actions recited in the claims may be performed in a differentorder and still achieve desirable results.

It will be understood that unless features in any of the particulardescribed implementations are expressly identified as incompatible withone another or the surrounding context implies that they are mutuallyexclusive and not readily combinable in a complementary and/orsupportive sense, the totality of this disclosure contemplates andenvisions that specific features of those complementary implementationsmay be selectively combined to provide one or more comprehensive, butslightly different, technical solutions. It will therefore be furtherappreciated that the above description has been given by way of exampleonly and that modifications in detail may be made within the scope ofthis disclosure.

1. An apparatus, comprising: an ultrasonic sensor array; a light sourcesystem; and a control system operatively configured to: control thelight source system to emit light, wherein the light induces acousticwave emissions inside a target object; select a first acquisition timedelay for the reception of acoustic wave emissions primarily from afirst depth inside the target object; and acquire first ultrasonic imagedata from the acoustic wave emissions received by the ultrasonic sensorarray during a first acquisition time window that is initiated at an endtime of the first acquisition time delay.
 2. The apparatus of claim 1,wherein the acquisition time delay is measured from a time that thelight source system emits light.
 3. The apparatus of claim 1, whereinthe first acquisition time window is in the range of about 10nanoseconds to about 200 nanoseconds.
 4. The apparatus of claim 1further comprising a substrate, wherein the ultrasonic sensor array isformed in or on the substrate and the light source system is coupled tothe substrate.
 5. The apparatus of claim 1, wherein light emitted by thelight source system is transmitted through the ultrasonic sensor array.6. The apparatus of claim 1, further comprising a display, wherein thecontrol system is further configured to control the display to depict atwo-dimensional image that corresponds with the first ultrasonic imagedata.
 7. The apparatus of claim 1, wherein the control system is furtherconfigured to select second through N^(th) acquisition time delays andto acquire second through N^(th) ultrasonic image data during secondthrough N^(th) acquisition time windows after the second through N^(th)acquisition time delays, each of the second through N^(th) acquisitiontime delays corresponding to a second through an N^(th) depth inside thetarget object.
 8. The apparatus of claim 7 further comprising a display,wherein the control system is further configured to control the displayto depict a three-dimensional image that corresponds with at least asubset of the first through N^(th) ultrasonic image data.
 9. Theapparatus of claim 1, wherein the control system is further configuredto select one or more wavelengths of the light to trigger acoustic waveemissions primarily from a particular type of material in the targetobject.
 10. The apparatus of claim 1, wherein the control system isfurther configured to estimate a blood oxygen level.
 11. The apparatusof claim 1, wherein the control system is further configured to estimatea blood glucose level.
 12. The apparatus of claim 1, wherein the controlsystem is further configured to control the light source system to emitat least one light pulse having a duration that is in the range of about10 nanoseconds to about 500 nanoseconds.
 13. The apparatus of claim 1,wherein the light source system includes at least one backlight or frontlight configured for illuminating a display and the target object. 14.The apparatus of claim 1, wherein the light source system includes oneor more laser diodes, semiconductor lasers or light-emitting diodes. 15.The apparatus of claim 1, wherein the light source system includes atleast one infrared, optical, red, green, blue, white or ultravioletlight-emitting diode or at least one infrared, optical, red, green, blueor ultraviolet laser diode.
 16. The apparatus of claim 1, wherein thecontrol system is capable of controlling the light source system to emita plurality of light pulses at a pulse frequency between about 1 MHz andabout 100 MHz.
 17. The apparatus of claim 1, wherein the firstultrasonic image data is acquired during the first acquisition timewindow from a peak detector circuit disposed in each of a plurality ofsensor pixels within the ultrasonic sensor array.
 18. The apparatus ofclaim 1, wherein the ultrasonic sensor array and a portion of the lightsource system are configured in one of an ultrasonic button, a displaymodule, or a mobile device enclosure.
 19. The apparatus of claim 1,wherein the control system is further configured to: acquire secondultrasonic image data at primarily the first depth inside the targetobject, the second ultrasonic image data acquired after the targetobject is repositioned on the apparatus; and stitch together the firstand second ultrasonic image data to form a composite ultrasonic image.20. The apparatus of claim 1, wherein the control system is furtherconfigured to acquire second ultrasonic image data primarily from thefirst depth inside the target object, the second ultrasonic image dataacquired after a period of time corresponding to a frame rate.
 21. Theapparatus of claim 1, wherein the control system is further configuredto acquire second ultrasonic image data from insonification of thetarget object with ultrasonic waves from an ultrasonic transmitter, thesecond ultrasonic image data acquired primarily from the first depthinside the target object, and wherein the first ultrasonic image dataand the second ultrasonic image data are acquired from a plurality ofsensor pixels within the ultrasonic sensor array.
 22. An apparatus,comprising: an ultrasonic sensor array; a light source system; andcontrol means for: controlling the light source system to emit light,wherein the light induces acoustic wave emissions inside a targetobject; selecting a first acquisition time delay to receive the acousticwave emissions primarily from a first depth inside the target object;and acquiring first ultrasonic image data from the acoustic waveemissions received by the ultrasonic sensor array during a firstacquisition time window that is initiated at an end time of the firstacquisition time delay.
 23. The apparatus of claim 22, wherein theacquisition time delay is measured from a time that the light sourcesystem emits light and wherein the first acquisition time window is inthe range of about 10 nanoseconds to about 200 nanoseconds.
 24. Theapparatus of claim 22, wherein the control means includes means forselecting second through N^(th) acquisition time delays and of acquiringsecond through N^(th) ultrasonic image data during second through N^(th)acquisition time windows after the second through N^(th) acquisitiontime delays, each of the second through N^(th) acquisition time delayscorresponding to a second through an N^(th) depth inside the targetobject.
 25. The apparatus of claim 22, wherein the control meansincludes means for estimating a blood oxygen level.
 26. The apparatus ofclaim 22, wherein the control means includes means for of estimating ablood glucose level.
 27. The apparatus of claim 22, wherein the controlmeans includes means for controlling the light source system to emit atleast one light pulse having a duration that is in the range of about 10nanoseconds to about 500 nanoseconds.
 28. The apparatus of claim 22,further comprising a display, wherein the light source system includesat least one backlight or front light configured for illuminating thedisplay and the target object.
 29. The apparatus of claim 22, furthercomprising a display, wherein the control means includes means forcontrolling the display to depict a two-dimensional image thatcorresponds with the first ultrasonic image data.
 30. A method ofacquiring ultrasonic image data, comprising: controlling a light sourcesystem to emit light, wherein the light induces acoustic wave emissionsinside a target object; selecting a first acquisition time delay toreceive the acoustic wave emissions primarily from a first depth insidethe target object; and acquiring first ultrasonic image data from theacoustic wave emissions received by a ultrasonic sensor array during afirst acquisition time window that is initiated at an end time of thefirst acquisition time delay.
 31. The method of claim 30, wherein theacquisition time delay is measured from a time that the light sourcesystem emits light and wherein the first acquisition time window is inthe range of about 10 nanoseconds to about 200 nanoseconds.
 32. Themethod of claim 30, further comprising controlling a display to depict atwo-dimensional image that corresponds with the first ultrasonic imagedata.
 33. The method of claim 30, further comprising: selecting secondthrough N^(th) acquisition time delays; and acquiring second throughN^(th) ultrasonic image data during second through N^(th) acquisitiontime windows after the second through N^(th) acquisition time delays,each of the second through N^(th) acquisition time delays correspondingto a second through an N^(th) depth inside the target object.
 34. Anon-transitory medium having software stored thereon, the softwareincluding instructions for controlling one or more devices to: control alight source system to emit light, wherein the light induces acousticwave emissions inside a target object; select a first acquisition timedelay to receive the acoustic wave emissions primarily from a firstdepth inside the target object; and acquire first ultrasonic image datafrom the acoustic wave emissions received by a ultrasonic sensor arrayduring a first acquisition time window that is initiated at an end timeof the first acquisition time delay.
 35. The non-transitory medium ofclaim 34, wherein the acquisition time delay is measured from a timethat the light source system emits light and wherein the firstacquisition time window is in the range of about 10 nanoseconds to about200 nanoseconds.
 36. The non-transitory medium of claim 34, wherein thesoftware includes instructions for controlling a display to depict atwo-dimensional image that corresponds with the first ultrasonic imagedata.
 37. The non-transitory medium of claim 34, wherein the softwareincludes instructions for: selecting second through N^(th) acquisitiontime delays; and acquiring second through N^(th) ultrasonic image dataduring second through N^(th) acquisition time windows after the secondthrough N^(th) acquisition time delays, each of the second throughN^(th) acquisition time delays corresponding to a second through anN^(th) depth inside the target object.